Security

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User Story

Grab a decent-size window with a decent-size page (e.g., <https://hg.mozilla.org/mozilla-central/rev/c9efa53d7aa9>).
Drag it to and from your external display from your MBP.
Watch how the contents of the window flicker between half-size (immediately after moving to hidpi) or double-size (after moving to lowdpi) and the correct scaling.
Testing with an old 30" Cinema Display and a late-2012 Retina MBP, and 2013-04-21's Nightly.